The present disclosure relates generally to well drilling and completion operations and, more particularly, to systems and methods of using electric motors to drive a drill bit.
To produce hydrocarbons (e.g., oil, gas, etc.) from a subterranean formation, wellbores may be drilled that penetrate hydrocarbon-containing portions of the subterranean formation. In traditional drilling systems, rock destruction is carried out via rotary power. This rotary power may be provided to the drill bit by rotating the drill string at the surface using a rotary table or a top drive. Alternatively, the drill bit may be independently rotated by a downhole mud motor irrespective of drill string rotation. Through these modes of power provision, traditional bits such as tri-cone, polycrystalline diamond compact (“PDC”), and diamond bits are operated at varying speeds and torques.
When using a mud motor to generate the torque for performing drilling operations, hydraulic losses along the drill string can limit the desired flow rate of mud. This in turn may reduce the hydraulic power one can apply to the mud motor to generate torque. This is especially relevant for drilling systems such as Reelwell™ where the flow rates are reduced to levels approaching 30% of conventional flow rates. The dramatic drop in flow rate coupled with greater depths of drilling targeted for this technology may result in higher fluid friction during circulation and thus the need for higher circulating pressures. Such a system may impose serious limitations on the hydraulic power available to the bottom hole assembly in ultra extended reach drilling.
In addition, special modifications to positive displacement motors (PDMs) are often required to permit these systems to operate at the lower flow rates. These modifications may involve lowering the fluid volume required to drive the power section per rotation of the mud motor rotor by reducing the volume of fluid per stage section of the mud motor. At these lower flow rates, turbine motors would need to have tighter vane structures with higher blade angles and higher flow velocities across the smaller vanes to operate effectively. This may result in higher flow resistance and a greater risk of erosion from the mud flow for a given operating output torque.
While embodiments of this disclosure have been depicted and described and are defined by reference to exemplary embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.